A study published this week in the American Journal of Preventative Medicine has confirmed what most people already know: fad diets don't work. Losing weight is a tedious process, and it requires major dietary changes and regular exercise. There are a variety of ways to interpret that advice, as the number of dieting options is almost limitless, and some aren't worth your time.

So, in the spirit of promoting science and ridiculing peddlers of nutritional silliness, here are the 4 worst fad diets to avoid if you want to get healthy and lose weight.

Eat Organic - Advocates of organic eating have made a habit of telling consumers that they are slowly killing themselves by eating conventionally produced food, but they are also fond of the idea that organic food encourages weight loss. The "hazardous toxins" found in conventional food that cause cancer and other assorted maladies also supposedly promote fat storage. The problem, however, is that there is no reason to think organic food is any healthier than conventional food. Indeed, this has been demonstrated many times in the last 50 years, and the reason is that "organic food" is a misnomer. All food is organic; what differs is the method used to grow food. And whether the contents of a salad were sprayed with natural or synthetic pesticides, eating a salad is definitely a healthier choice than eating a snickers bar. Weight loss comes down to the nutritional content of the food people eat, not how it was grown.

Vegetarianism - Vegetarian diets are thought to promote weight loss because they are low in fat and calories, the two nutritional bogeymen most demonized today. If people avoid fat and limit their caloric intake, the thinking goes, they can stay in shape and avoid medical conditions like heart disease. The "meat causes heart disease" hypothesis has been tackled on PolicyMic previously, but there's another problem with vegetarianism. Because animal products contain a number of important nutrients, removing them from the diet can be dangerous. Furthermore, any weight loss achieved on a vegetarian diet is probably due to the fact that vegetarians rarely or never consume the sugar-laden foods (Twinkies, soda, etc.) that are most responsible for weight gain. There is nothing magical about tofu or carrots as far as weight loss is concerned.

Gluten-Free Diets - Thanks to pop star Miley Cyrus, the health and nutrition world is buzzing about a gluten-free diet as a means to lose weight. Cyrus tweeted this week that she slimmed down by switching to a gluten-free diet, and called the protein "crapppp." Gluten is found in grains like wheat, barley, and rye; and it gives baked goods the chewy texture that most consumers find desirable. Diets excluding gluten are recommended for people with celiac disease, but there is little reason to think that avoiding gluten by itself will encourage weight loss. Any diet too high in grains raises blood sugar, which encourages fat storage. People on gluten-free diets can consume a variety of grains and starches (rice or potatoes, for example) that raise blood sugar. Eating too much of these foods is a good way to gain weight, no matter how little gluten a person consumes.

"Eat less, move more" - Promoted by everybody from the soda industry to the federal government, call this the fad diet that won't die. The eat less, move more diet stresses that weight is simply a matter of energy imbalance. Consuming too many calories causes weight gain, so the solution is to eat fewer and burn more. This advice has been gospel for decades despite the contrary evidence that has piled up during that same period. Of course, overeating isn't a good idea, but the question has to be asked: why do people overeat in the first place? The likely reason is that the human body doesn't treat all calories the same, and eating too many unhealthy calories will make people fat and keep them that way.